Within the last decade, an amount of literature has been published describing various polycrystalline, microcrystalline, or non-vitreous fibers and other shaped articles of refractory metal oxides. These articles are made by various non-melt processes, such as by drying films of solutions of metal oxide precursors or oxide sols, or drying organic polymeric bodies, such as cellulose or rayon, impregnated with such a solution, or by extruding and drawing, or spinning, viscous fluids of such metal compounds into fibers. The fibers are then heated to remove water, organic material, and other volatile material to produce a refractory article. A review of the state of the art of polycrystalline inorganic fibers appears in Chapter 8 of "Modern Composite Materials" edited by Broutman and Krock, published by Addison-Wesley Pub. Co., Reading, Mass. (1967). Other art in this area is Netherlands Pat. No. 7,015,245, British Pat. No. 1,287,288, U.S. Pat. Nos. 3,385,915, 3,632,709, 3,663,182 and the art cited in U.S. Pat. No. 3,709,706. Oxide fibers other than those identified as fiberglass are still in the relatively early stage of development. In many technologies, there is a need for a relatively inexpensive continuous refractory fiber product with desirable physical properties, such as high strength, high modulus of elasticity, chemical resistance, and the retention of such properties after exposure to high temperatures beyond the capability of presently commercially available fiber materials.
Bicomponent fibers are known in the textile art. Typical bicomponent polymer textiles are disclosed in U.S. Pat. Nos. 4,118,534 and 4,278,634. Generally, polymer bicomponent systems relate to two polymers of the same class, e.g., two polyester polymers, or two acrylonitrile polymers. Usually different polymers in a bicomponent system will split after spinning.
Blown-microfibers (3 to 5 micrometer diameter) comprising bicomponent systems, i.e, polyester-polypropylene have been disclosed in U.S. Ser. Nos. 704,537 and 540,544. Blowing such fibers requires use of a Naval Research Laboratories dual feed die.
U.S. Pat. No. 2,313,296 teaches concentrically disposed fibers or filaments of glass. These fibers do not crimp.
It is well-known in the art to prepare monocomponent ceramic fibers from spinning sols. For example, alumina-silica fibers are disclosed in U.S. Pat. No. 4,047,965; alumina-boria-silica fibers are taught in U.S. Pat. No. 3,795,524; titanium dioxide fibers are disclosed in U.S. Pat. No. 4,166,147; zirconia-silica fibers are disclosed in U.S. Pat. No. 3,709,706.